The present invention generally relates to control of electrical power distribution and more particularly, employment of high voltage direct current (HVDC) contactors for switching under conditions in which a DC load may be present in a circuit.
There is a growing need for HVDC power distribution systems in vehicles. For example, use of HVDC electrical power on aircraft such as the so-called More Electric Aircraft (MEA) is potentially attractive for low-loss distribution while maintaining relatively low electrical system weight.
Some of the challenges associated with the use of HVDC systems include improving the reliability and reducing size and weight of key components in the power distribution system, such as electric load control units (ELCUs) or remote power controllers (RPCs) for load control and feeder protection, and primary bus switching contactors, which mainly operate on an electromechanical principle. These current interrupting devices generally include a pair of mechanical contacts between the HVDC source and a load path which can rapidly separate either by means of electromechanical force upon an open command, or when mechanically “bouncing” during a closing transition upon a close command. When the contacts become separated, an electric arc may form as a result of the inductive energy stored in the connected circuit. Unlike AC applications, where the arc is self extinguished due to zero crossing of the AC current, the arc generated in an HVDC contactors will continue to carry current until the current eventually ceases as result of further opening of the contacts. This generates heat in the contact area and gradually erodes the surface of the contacts after repeated application. Use of higher operating voltages exacerbates this phenomenon. Various methods have been developed for HVDC contactors to suppress arcing using different arc chamber configurations and materials, which are structured to rapidly increase arc voltage. Also hybrid HVDC contactor concepts have been proposed whereby semiconductor switching devices are connected in parallel with the main electromechanical power switching contacts to bypass (or absorb) the entire energy generated during the switching transients, which would, otherwise, cause an arc. Some prior art HVDC contactors may employ positive temperature coefficient (PTC) materials connected in parallel with the main electromechanical contacts to convert the arc energy generated during contactor switching operation into heat dissipated in the PTC device.
As can be seen, there is a need to provide improved hybrid HVDC contactors and HVDC circuit interruption techniques. In particular there is a need to provide for circuit interruption with controlled arc energy